Brookline's brand-new fire truck spent the last week at a Walpole dealership while mechanics tried to figure out what caused it to break down in the middle of the street last Thursday.

Fire Chief Peter Skerry said mechanics now believe a faulty fuel injector is to blame for the breakdown, which left the truck stranded on Station Street for four hours, and have ordered a part from Wisconsin. He expects the $900,000 vehicle will be back on the street in Brookline by tomorrow.

"It's such a complicated piece of machinery, to some extent malfunctions are expected on any piece of apparatus no matter how new it is," Skerry said.

The truck, called a quint, is a hybrid of a fire engine and ladder truck and was put into service last May. Fire fighters are using a spare fire engine while the 6-month-old vehicle is in the shop.

The quint's breakdown last Thursday came the same day a spare ladder truck in the Brookline Village Fire Station caught fire and had to be towed away. Skerry said the disabled quint sat on Station Street for four hours while mechanics tried to diagnose the problem before it was towed to the same dealership where the scorched ladder truck was repaired.

"When it rains, it pours," said Skerry. "We had two vehicles break down on us in the space of about three hours."

Skerry said the quint is still under warranty and the town will pay nothing for the repairs or the cost of towing it to the dealership. He said it didn't worry him that the vehicle broke down in the middle of a run just six months after it had been put on the street.

"If it was anything of a repetitive nature, the same thing breaking down over and over, or we heard it had the same problem with different fire departments, then I'd be concerned," he said. "But I'm not concerned about this."